THE VEGETABLE PARASITES. 43 



Now, one drop of the fluid thus prepared, and in which 

 the first degree of attenuation is produced, is put into 

 another vessel containing fowl broth and placed under the 

 same conditions as the first. This process is repeated until 

 the requisite degree of attenuation is reached. The 

 greater the intervals which elapse between each cultivation, 

 and the greater the number of cultivations, the less virulent 

 will the culture become. 



The ' vaccine ' may be injected into the subcutaneous 

 tissue. Great care is required in obtaining the requisite 

 degree of attenuation. 



Large numbers of sheep and other animals have been 

 thus inoculated by Pasteur, and the results of his labours 

 attest the practical value of his investigations. 



Quite recently M. Pasteur has notified that he has been 

 able to confer immunity from hydrophobia by inoculating 

 with the attenuated virus of this disease. 



The Blastomycetes or Yeasts. — These are roundish or 

 oval cells which sometimes form chains by joining end to 

 end. 



The yeasts multiply by gemmation, or when food is not 

 abundant by the formation of spores in the interior of the 

 cells. They never invade living tissues, and are of far less 

 importance in the causation of disease than the Schizomy- 

 cetes or Bacteria and the Hyphomycetes or Moulds. As an 

 example of the group of yeasts may be mentioned the 

 Oidium Albicans. 



The Hyphomycetes or Moulds. — These consist of fila- 

 ments called hypha?, formed by a single row of cells placed 

 end to end, growing by means of an apical cell which elon- 

 gates and divides transversely. 



The Thallus usually consists of numerous hypha?, though 

 it may be formed of one only. Several skin diseases are to 

 be attributed to invasion by these vegetable parasites. 



