ETIOLOGY OF SPLENIC FEVER.
M. Pasteur had triumphed over splenic fever with as much rigour as precision. But he considered that he had still to make one further investigation. He had established the effects of the pest; he had discovered a preventive method with which to combat it: he now wished to know the origin of the evil. Whence comes splenic fever? Why is it endemic in certain departments of France, in certain parts of Russia, Germany, Austria, Italy, Spain, and America? How is it sustained? It was for a long time believed that splenic fever was born spontaneously under the influence of various accidental causes. M. Bouley has related, in his learned work on the 'Progress of Medicine by Experimentation,' that in 1842 the Minister of Agriculture, M. Cunin-Gridaine, at the request of the deputies of the departments that were ravaged by the epidemic, entrusted to M. Delafond, a professor of the school at Alfort, the task of investigating this malady, commonly called the 'blood disease,' in the districts in which it was raging. He was to search out its causes, and ascertain whether they did not result from the system of cultivation prevalent in the country.
M. Delafond arrived in Beauce. One fact struck him—namely, that almost all the animals attacked by the disease were young, fine, and vigorous: those, in short, that gave the best promise. Viewing the richness of the soil and the abundance and quality of the crops in conjunction with this observation, Delafond at once elaborated a speculative theory. 'The blood disease,' said he, 'is nothing but an overfulness—an excess of blood circulating in the vessels, and especially the predominance in that liquid of red globules.'
Starting from this idea, his one object was, by means of logical deduction, to trace everything to this fundamental error. He analysed the soil, and demonstrated to what extent it was fitted to furnish crops that were rich and abounding in nutritive properties. He analysed the plants. He then complacently referred the richness of blood of the Beauce sheep to the richness in nitrogenous principles of the substances on which they were fed. He examined the lesions of the diseased animals, and concluded that they were the consequence of the blood containing too large a proportion of the organic elements, called globules, fibrine, albumen, and too small a proportion of water.
'Reduce the proportion of nutritious elements,' he wrote as his advice to the agriculturists, 'mix roots with all that is too rich in nitrogenous principles, and you will reduce in proportion the losses caused by the excess of the ultra-nutritious substances with which you supersaturate your cattle.'
'Such is the very logical conclusion to which Delafond was led,' adds M. Bouley, ridiculing these observations, based on a method of reasoning, instead of on the experimental method. 'And as a fresh proof of his theory he mentions the fact that the disease decreases as you descend the country towards the Loire. On the right bank of that river—in Sologne, for instance, which is a low, sandy, damp district—blood disease is unknown. In the arrondissements of Gien and Montargis and in parts of those of Orleans and Pithiviers it prevails but little. There, Delafond imperturbably remarks, the soil is sandy and the herbage not nearly so rich as in the Beauce plateau; and there the blood disease is consequently less common.'
When we consider that such opinions could be written unchallenged only forty years ago, that they could even borrow a scientific character from the inspiration that gave them birth, we can see the progress that has since been made, and can realise how great were the obscurity and uncertainty which have been dispelled by the experimental method.
The presence of a parasite having been brought to public notice in the blood of animals suffering from splenic fever, at the very time when Pasteur had shaken the belief in spontaneous generation, people grew accustomed to the idea that the stricken animals might have contracted the germs of the malady from the outer world, without any spontaneous birth, strictly so called, of the disease. This opinion was strengthened by a knowledge of the spores of the splenic bacillus. Pasteur, aided by Messieurs Chamberland and Roux, commenced experiments with a view to solving this difficult etiological question. The first experiments took place in the fields of a farm at the village of St. Germain, near Chartres. Several groups of sheep were fed on lucern grass which had been sprinkled with artificially-reared splenic fever bacteria, or with their germs or spores. Although all the sheep of the same group absorbed an immense number of the spores of the parasite, many survived, even after being visibly affected. Those that died showed all the symptoms of what is called spontaneous splenic fever. The period of incubation lasted as long as eight or ten days, although, in its latter stages, the disease exhibited those startling features which have caused a belief that the incubating period is a very short one—short, that is to say, for those conditions of contagion where the parasite is not deposited in its pure state under the animal's skin.