PATHOGENIC PROTOZOA. 425 



ditions, and al o in vaccine lymph, and in emulsions from tissues and in exudates. 

 He therefore regards them as for the most part, if not wholly, products of degen- 

 erating tissue cells and of leukocytes. 



YELLOW FEVER. 



It has already been indicated (page 149) that the study of cases of yellow 

 fever has failed to prove that this disease is caused by bacteria. On the other 

 hand, evidence that it is transmitted by the mosquito, Stegomyia, has been 

 increasing. 



Piroplasma Bigeminum, Pirosoma Bigeminum, Apio- 

 soma Bigeminum. Theobald Smith was the first to describe 

 this parasite which is found in the blood of cattle suffering with 

 cattle fever, though Babes reported having found certain cell 

 inclusions in the blood of sick cattle in Roumania, and Smith 

 and Kilborn made extensive studies of the organism. It is 

 pear-shaped occurring in pairs with the pointed end toward 

 each other, each half of the pair is 2 to 4 mikrons long, by i^- 

 to 2 mikrons wide. It occurs inside the red corpuscles. 

 Pseudopodia are described by Nuttall and Graham-Smith.* 

 It stains well with the basic dyes and is well brought out by 

 Romanowsky. It has never yet been cultivated. It is spread 

 from sick to diseased animal by a tick, Boophilus bovis sive 

 annulatus, in America, by several species of ticks apparently 

 in Germany. The ticks seem to serve merely as carriers, 

 the organism appears to undergo no development in the body 

 of the tick. Other animals than cattle also suffer from 

 infection with organisms of similar description. Sheep, dogs, 

 horses, and apes have been found to harbor a parasite of 

 this character. It has been stated that men have also been 

 found with a similar organism in the blood in cases of " Spotted 

 fever" in Montana as reported by Wilson and Chowning.t 

 But StilesJ failed to corroborate this statement. Ricketts 

 found that the disease is transmitted by a tick, Dermacentor 



*Journ. Hygiene. Vol. VI. 1906. p. 586. 



tRep. Montana State Board of Health. 1901-2. Also Journ. Inject. Dis- 

 eases. Vol. I., No. I. Jan. i, 1904. pp. 31-57- 

 J Pub. Health and Mar. Hosp. Bull. No. 20, 1905. 

 \Journ. Inject. Dis. Vol. IV , No. i. Jan. i, 1907. pp. I4I-I53- 



