38 SPOKOZOA. 



Oocysts of CocciDiA escaping in the faeces in an incompletely 

 developed condition may be observed to complete their 

 development, especially when mixed with a 5 per cent, 

 solution of bichromate of potash. Malarial parasites, when 

 observed as described above, Avill continue to develop for 

 several hours, and the production of merozoites can sometimes 

 be observed. Occasionally the removal of the blood from 

 the Vertebrate host may induce the development of stages 

 which normally take place inside the body of an Invertebrate 

 host : thus the production of gametes from the gametocytes, 

 fertihzation, and the development of ookinetes may be followed 

 in a drop of blood enclosed between a sHde and a cover -glass. 

 During the observations the cover-glass may be removed and 

 permanent preparations made showing particular stages of 

 development. 



When the body-fluid containing the parasites is too small in 

 amount to make a suitable preparation, physiological salt 

 solution (0-7 per cent, solution of sodium chloride in distilled 

 water for cold-blooded animals and 0-85 or 0-9 per cent, 

 solution for warm-blooded animals) or Ringer's solution may 

 be added. Ringer's solution consists of sodium chloride 

 0'8 grm., potassium chloride 0-02 grm., calcium chloride 

 0-02 grm., sodium bicarbonate 0-02 grm., distilled water 

 100 c.c. 



Intra-vitam Staining. — Examination of the hving organisms 

 is facihtated by intra-vitam staining, different parts of the 

 organism or its contents being coloured without kilHng the 

 animal or affecting its movements. For this purpose neutral 

 red or methylene blue are used in very dilute solutions 

 (1 in 10,000). A drop of the stain may be allowed to dry 

 on the slide and the fluid containing the organisms be placed 

 on the area and covered with a cover-glass. The stains are 

 slowly absorbed by the parasites. Neutral red assumes 

 a bright cherry-red colour in acid and a brown colour in 

 alkaline media, and thus serves to indicate the reaction of the 

 substance which it stains. 



Eosin is used as an indicator of the life or death of an 

 organism. It will not stain hving cytoplasm, and by running 

 a dilute solution under the cover-glass the Uving organisms 

 can be distinguished from those that are dead. 



Cultivation. — Various methods have been adopted to provide 

 favourable conditions of growth and multiphcation, so as to 

 afford large numbers of a particular organism outside the body 

 of the host for extensive study or for the purposes of a class. 

 No artificial medium has so far been discovered in which 

 Gregarinida or Coccidia will grow : but various methods 

 have proved successful for the cultivation of blood-inhabiting 

 parasites, as the malarial parasites and the Piroplasmids. 



