On the mode of communication of cholera

by John Snow

“Stockport. (Dr. Rayner and Mr. J. Rayner, reporters). Sarah Dixon went to Liverpool, September 1st, to bury her sister, who had died of cholera there; returned to Stockport on September 3rd; was attacked with cholera on the 4th; was taken home by her mother to her mother’s house, a quarter of a mile distant; was in collapse, but recovered. Her mother was attacked on the 11th, and died. The brother, James Dixon, came from High Water to see his mother, and was attacked on the 14th.

“Liverpool. (Mr. Henry Taylor, reporter.) A nurse attended a patient in Great Howard Street (at the lower part of the town), and on her return home, near Everton (the higher part of the town), was seized, and died. The nurse who attended her was also seized, and died. No other case had occurred previously in that neighbourhood, and none followed for about a fortnight.

“Hedon. (Dr. Sandwith, reporter.) Mrs. N. went from Paul, a village close to the Humber, to Hedon, two miles off, to nurse her brother in cholera; the next day, after his death, went to nurse Mrs. B., also at Hedon; within two days was attacked herself; was removed to a lodging-house; the son of the lodging-house keeper was attacked the next day, and died. Mrs. N.’s son removed her back to Paul; was himself attacked two days afterwards, and died.”

It would be easy, by going through the medical journals and works which have been published on cholera, to quote as many cases similar to the above as would fill a large volume. But the above instances are quite sufficient to show that cholera can be communicated from the sick to the healthy; for it is quite impossible that even a tenth part of these cases of consecutive illness could have followed each other by mere coincidence, without being connected as cause and effect.

Besides the facts above mentioned, which prove that cholera is communicated from person to person, there are others which show, first, that being present in the same room with a patient, and attending on him, do not necessarily expose a person to the morbid poison; and, secondly, that it is not always requisite that a person should be very near a cholera patient in order to take the disease, as the morbid matter producing it may be transmitted to a distance. It used to be generally assumed, that if cholera were a catching or communicable disease, it must spread by effluvia given off from the patient into the surrounding air, and inhaled by others into the lungs. This assumption led to very conflicting opinions respecting the disease. A little reflection shews, however, that we have no right thus to limit the way in which a disease may be propagated, for the communicable diseases of which we have a correct knowledge spread in very different manners. The itch, and certain other diseases of the skin, are propagated in one way; syphilis, in another way; and intestinal worms in a third way, quite distinct from either of the others.

A consideration of the pathology of cholera is capable of indicating to us the manner in which the disease is communicated. If it were ushered in by fever, or any other general constitutional disorder, then we should be furnished with no clue to the way in which the morbid poison enters the system; whether, for instance, by the alimentary canal, by the lungs, or in some other manner, but should be left to determine this point by circumstances unconnected with the pathology of the disease. But from all that I have been able to learn of cholera, both from my own observations and the descriptions of others, I conclude that cholera invariably commences with the affection of the alimentary canal. The disease often proceeds with so little feeling of general illness, that the patient does not consider himself in danger, or even apply for advice, till the malady is far advanced. In a few cases, indeed, there are dizziness, faintness, and a feeling of sinking, before discharges from the stomach or bowels actually take place; but there can be no doubt that these symptoms depend on the exudation from the mucous membrane, which is soon afterwards copiously evacuated. This is only what occurs in certain cases of hæmorrhage into the alimentary canal, where all the symptoms of loss of blood are present before that fluid shows itself in the evacuations. In those rare cases, called “cholera sicca,” in which no purging takes place, the intestines have been found distended with the excretion peculiar to the disease, whenever an examination of the body has taken place after death. In all the cases of cholera that I have attended, the loss of fluid from the stomach and bowels has been sufficient to account for the collapse, when the previous condition of the patient was taken into account, together with the suddenness of the loss, and the circumstance that the process of absorption appears to be suspended.

The symptoms which follow the affection of the alimentary canal in cholera are exactly those which this affection is adequate, and, indeed, could not fail to produce. The analyses which have been made of the blood of cholera patients, show that the watery fluid effused into the stomach and bowels is not replaced by absorption, or is replaced only to a small extent. The analyses of Dr. O’Shaughnessy and others, during the cholera of 1831–32, show that the amount of water in the blood was very much diminished in proportion to the solid constituents, and that the salts of the blood were also diminished. The analyses of Dr. Garrod and Dr. Parkes, in the spring of 1849, were more numerous and exact.[^[3]] The amount of water in the blood of healthy persons is on the average 785 parts in 1000; whereas, in the average of the analyses performed by Drs. Garrod and Parkes, it was only 733 parts, while the amount of solid constituents of the blood, relatively to the water, was increased from 215—the healthy standard—to 267. The globules, together with the albumen and other organic constituents of the serum, amount in the healthy state to 208 parts in 1000, while in the blood of cholera patients they amounted to 256 parts. The saline constituents in 1000 parts of blood are somewhat increased, on account of the great diminution of water; but, when estimated in relation to the other solid ingredients, or to the whole quantity existing in the healthy body, the amount is diminished. Dr. Garrod is of the opinion that a chemical analysis will determine whether or not a specimen of blood has been derived from a cholera patient.

The stools and vomited matters in cholera consist of water, containing a small quantity of the salts of the blood, and a very little albuminous substance. The change in the blood is precisely that which the loss by the alimentary canal ought to produce; and, indeed, it is physically impossible that the alteration in the blood can be caused in any other way. The sweating which takes place in an advanced stage of the disease may increase the density of the blood to a trifling extent; but it does not come on till the blood is already altered, and it is only a consequence of the diminished force of the circulation, like the sweating met with in collapse from hæmorrhage or severe injuries, and in faintness from venesection.

The loss of water from the blood causes it to assume the thick tarry appearance, so well known to all who have opened a vein in cholera. The diminished volume of the blood causes many of the symptoms of a true hæmorrhage, as debility, faintness, and coldness; while these effects are much increased by its thick and tenacious condition, which impedes its passage through the pulmonary capillaries, thereby reducing the contents of the arteries throughout the system to the smallest possible amount, as indicated by the small thready pulse. The interruption to the pulmonary circulation occasioned by the want of fluidity of the blood, is the cause of the distressing feeling of want of breath. Proofs of the obstructed circulation through the lungs generally remain after death, in the distended state of the pulmonary arteries and right cavities of the heart. The deficient supply of blood to the various organs, and its unfitness to pass through the capillaries, are the cause of the suppression of the renal, biliary, and other secretions. The cramps appear to consist chiefly of reflex action, caused by the irritation, and probably the distension, of the bowels.

If any further proof were wanting than those above stated, that all the symptoms attending cholera, except those connected with the alimentary canal, depend simply on the physical alteration of the blood, and not on any cholera poison circulating in the system, it would only be necessary to allude to the effects of a weak saline solution injected into the veins in the stage of collapse. The shrunken skin becomes filled out, and loses its coldness and lividity; the countenance assumes a natural aspect; the patient is able to sit up, and for a time seems well. If the symptoms were caused by a poison circulating in the blood, and depressing the action of the heart, it is impossible that they should thus be suspended by an injection of warm water, holding a little carbonate of soda in solution.