^02 THE AMERICAN MONTHLY [Jul 



tirely demolished by experiments, which proved that the 

 disease was caused by young ticks hatched from the eggs 

 of the mature ticks which developed upon the Southern 

 cattle, that is, the contagion is in some manner transmit- 

 ted from the adult tick through its eggs to its progeny, 

 and this progeny has the power of inserting the conta- 

 gion into the circulation of the cattle upon which it hap- 

 pens to fasten itself. 



These facts threw much liglit upon the propagation of 

 the malady, but they were not suflBcient to establish a 

 scientific theory explaining the transmission. Indeed, it 

 was yet to be proved that the Southern cattle carried the 

 protozoa in their blood. Microscopic examination was not 

 sufficient to decide the question. A few minute points 

 were observed in the red corpuscles of Southern cattle, 

 but these points were much smaller and far less numerous 

 than the protozoa in sick Northern cattle. The Southern 

 cattle, besides were in good health, and it seemed improb- 

 able that they harbored so deadly a parasite. 



There was but one way to decide as to whether South- 

 ern cattle carried this contagion in their blood, and that 

 was to inoculate susceptible Northern cattle with the 

 blood of Southern cattle. This experiment was made, and 

 it demonstrated that a comparatively small quantity of 

 blood from a Southern cow, injected under the skin or in- 

 to the veins of Northern cattle, produced an acute attack 

 of Texas fever. In Northern cattle infected in this man- 

 ner the protozoa appeared in the blood corpuscles with the 

 same characteriaticsas when the infection occurred through 

 the medium of ticks. There could no longer be any doubt 

 that the blood of cattle from the infected district contain- 

 ed the contagion of Texas fever. 



It was now important to decide how long Southern cat- 

 tle carried this contagion in their blood after leaving the 

 infected district. Again, it was necessary to resort to in- 

 oculation, as the microscope was powerless to decide. The 



