1920.] NATURAL SCIENCES OF PHILADELPHIA. 331 



STATISTICAL OBSERVATIONS ON THE TEXAS FEVER PARASITE. 



BY HOWARD CRAWLEY. 



The study herein described was based on material obtained from 

 two cows, Nos. 1025 and 1031, of the series of the Experiment Sta- 

 tion of the United States Bureau of Animal Industry. These, being 

 so-called northern animals, were susceptible to Texas fever, and 

 were both inoculated with this disease by infestation with infectious 

 seed ticks on June 27, 1913. Cow No. 1031 died on July 10, and a 

 series of preparations was obtained shortly after death from the 

 heart muscle, the hver, the spleen, and the kidney. Cow No. 1025 

 died July 11, and a set of smears was obtained from the heart muscle. 



The morphology of the Texas fever parasite, for which the correct 

 name appears to be Babesia hovis, has been described a number of 

 times and is in consequence a matter of common knowledge. This 

 phase of the biology of the organism was therefore not studied, but 

 since the material obtained, especially from Cow 1031, was rich in 

 parasites and parasitized cells, a statistical investigation was under- 

 taken. This had to do, first, with the relative numbers of paras- 

 itized and non-parasitized cells; second, with the number of indi- 

 vidual parasites in each parasitized cell; third, with the varying 

 conditions found in the several organs of Cow 1031 ; finally, a 

 count was made of the parasites occuring free in the preparations. 

 The exact significance of these latter is somewhat problematical, 

 since, theoretically, they may either represent elements escaped from 

 a blood cell, or merely what remains after the blood cell has been 

 destroyed.' The latter supposition seems the more probable, since 

 these parasites, like those within the cells, may occur either singly 

 or in multiple form. Indeed, the fact that these apparent free 

 parasites occur in multiple form rather suggests that they are still 

 lying in some remant of the blood cell which does not stain. The 

 impression received from an examination of this material is that 

 these "free" parasites have no especial significance, and are to be 

 placed in the same category as those still lying in intact blood cells. 



The smears were fixed in alcohol and stained with Giemsa. The 

 method of study was very simple. A small square was cut on a 



