28 SOME MINUTE ANIMAL PARASITES 



threadlike portion forms near the blepharoplast, 

 and gradually this thread, or flagellum, reaches the 

 surface (Fig. 6), pushing the outer layer before 

 it, and so producing the characteristic undulating 

 membrane. The posterior end lengthens at the 

 same time, and ere long the trypanosome has fully 

 formed, and swims away into the general circulation. 

 Some trypanosomes ultimately find their way into 

 the cavities of the spinal cord and brain, and there 

 continue their activities, producing the sleepiness 

 that deepens and deepens until it reaches the infinite 

 sleep of death. 



In spite of the enormous difficulty of the work, the 

 formation of the latent bodies from the flagellate 

 trypanosomes and the growth of the latent bodies 

 into the flagellate forms has been observed in the 

 living organisms by one of the present writers 

 (H. B. F.), who described the processes fully in a 

 paper read before the Royal Society in December, 

 1910, and published in the Proceedings of that 

 Society in 1911. 



In 1910, Sir Ronald Ross and Dr. D. Thomson 

 counted daily the number of trypanosomes present 

 in definite quantities of the peripheral blood of a 

 patient, and plotted a curve, showing the relations 

 of the daily numbers. They found that every seven 

 days there was a crest in the curve, showing that the 

 number of trypanosomes reached a maximum every 

 seventh day. After this there was a decrease to 

 a minimum, and then again an increase to a maxi- 

 mum. This same periodic variation in the numbers 

 of flagellate trypanosomes was found to occur in 



