114 PROTISTS AND DISEASE 



prepared beforehand. All the preparations gave positive 

 results. 



I was able to demonstrate the movement on the third, 

 fourth, fourteenth, and fifteenth days to seven different 

 trained observers, four of whom are expert in pathology. 

 In these demonstrations the movement was shown under a 

 magnification of 500 diameters with a dry objective. The 

 oil-immersion lens when used for preparations simply 

 mounted in water has the drawback of dragging on the 

 cover-glass and causing movements in the objects beneath it. 



This set of preparations I last examined on the thirty- 

 fifth day after making the cultures. On this occasion 

 commotion was present in a few only of the corpuscles, and 

 the rest were obviously degenerating and becoming stained 

 by the colouring matter of tea-leaves on which they were 

 placed. So long as they remain in full vitality they do not 

 absorb the colouring matter. 



In addition to facts mentioned above, Fig. 31 shows 

 the appearance and distribution of contaminating bacteria 

 in molluscum cultures. 



To anticipate what will become clear after smallpox, 

 syphilis and cancer have been considered in Chapter X, it 

 may be observed that Plassomyxa contagiosa passes through 

 certain phases in water outside the host-body, whereas the 

 parasites of smallpox &c. pass through the corresponding 

 phases inside the host-body. 



The Incubation-Period of the Filtered Virus. One of the 



