12 BACTERIOLOGY 



Yeasts. These possess neither spore-bearing organs 

 nor spores, but multiply by gemmation, which consists in 

 the budding out of daughter-cells in different places from 

 the gradually enlarging mother-cell, these in their turn be- 

 coming mother-cells, thus forming groups of buds. The 

 individual yeast-cells are round or elliptical, and often 

 display in their interior colourless lacunae, which are not 

 spores, but may perhaps consist of minute drops of fat, 

 and are called vacuoles. The yeasts play an important 

 part in nature in causing fermentation. Several species 

 of them form pigments. 



Algae. Of these the cladothrix, crenothrix, and becj- 

 giatoa varieties belong to the micro-organisms. They are 

 jointed filaments, which multiply not by fission but by 

 germination at their extremities (fig. 7). 



Protozoa. Of the protozoa those important as regards 

 bacteriological investigation are the sporozoa, which include 

 the gregarince, psorospermii, and coccidia. They are 

 unicellular organisms which can only live in a moist or 

 liquid medium, and in the absence of water, nutrient 

 material, or oxygen, are transformed into roundish durable 

 cysts. They possess a sort of larval condition, consisting 

 of irregular and roundish little masses of protoplasm, 

 which move by means of processes projecting oat like 

 limbs (pseudopodia) , or by flagella, and often, losing their 

 mobility, take up a permanent residence in other cells. 

 The contents of the cyst separate by division or gemmation 

 into particles called sporocysts or psetidonawceUa, the 

 contents of which, again, break up into a number of sickle- 

 shaped germs. Pfeiffer considers the plasmodia of malaria 

 to be also cysts of this nature containing crowds of spores. 



Examination of micro-organisms. Microscopic examina- 

 tion alone is not sufficient to establish fully the properties 

 of micro-organisms in their morphological and biological 



