He claims to have made a further success in cultivating the parasite in ox-blood serum highly charged with hæmoglobin. It was only occasionally, and by the use of blood extraordinarily rich in the parasites, that success was obtained. In one such case he produced five successive cultures, the product being the rounded forms only and within these the germs. There were no piriform bodies. These are not formed outside of the red globules. The third successive culture in this medium grew with great readiness, producing larger parasites with less disposition to contract, but the fourth and fifth cultures were encreasingly poor. Inoculation with these cultures failed to produce the disease. To explain this the doctrine of passive germs, strong for survival, but weak pathogenically, is hazarded.
To summarize, the successive stages of the piroplasma are: 1st. The intraglobular pear-shaped bodies, with flagellum often connecting two bodies. 2nd. The rounded bodies with refrangent nucleus—intraglobular or extraglobular. 3d. The free round bodies with the nucleus divided into 2 to 5 chromatin masses. 4th. The free chromatin masses, large, active, infecting germs, and small, passive, noninfecting germs. The insuccess of inoculations of cattle with the last-named bodies throws an air of doubt upon them as links in the pathogenic chain. Definite information on the antecedents, environment, food, etc., of the cattle unsuccessfully inoculated, including the season, shelter and meteorological conditions might have brought us a step nearer to the full life history of the piroplasma.
The Cattle Tick: Boöphilus Bovis: Ixodes Bovis: I. Dugesii: The Invertebrate Host of the Texas Fever Organism. As early as 1868 shrewd observers had noticed that in all outbreaks of Texas fever the affected animals were covered with ticks, and drew the natural inference that the disease was due to the bites of these insects. But the prevalence of ticks in localities where the disease was unknown served to draw attention away from the important fact that was suggestive of the true explanation of the disease. The truth, however, constantly obtruded itself that casual cases were never found in the absence of the tick. Finally, in 1889, Kilborne conceived the idea of putting the matter to the test, and with the approval of the Chief of the Bureau of Animal Industry, set aside special paddocks for this purpose. Five native cattle were placed, at midsummer, with three South Carolina cattle, from which all ticks had been carefully picked, and they completely escaped infection.
After seventy-one days, on September 6th, when the hottest weather had passed, two were turned into a lot with four South Carolina cattle of the original herd which had stocked the pasture with ticks. Of the two one died of Texas fever, September 20th, and the other sickened in the last week of September, and had a relapse in October, but finally recovered. Of eleven other native cattle placed in this tick-infested field up to September 30th, ten sickened and one escaped. One animal placed in the field October 19th escaped.
Again three North Carolina cattle and three natives were placed in a field September 14th and 15th. The new generation of ticks was retarded by the cool season, so that few larvæ appeared on the native stock yet one of the three sickened.
These results were confirmed by a series of other similar experiments.
In a further experiment, September 13th, thousands of ticks, mostly mature, from North Carolina, were scattered over a second lot and four native cattle turned into it next day. Three sickened and one, to outward appearance, escaped.
These results were corroborated by experiments made in succeeding years. In addition the disease was produced regularly in native stock by placing on their skin the six-legged larvæ of boöphilus bovis, which had been hatched in glass vessels in the laboratory. It was also shown that the Washington winter destroyed the ticks in infected pastures so that native cattle could be safely turned on them the following spring or summer.
To summarize:—
1. The blood of southern cattle containing the piroplasma produced the disease when injected into a healthy susceptible animal.