156 GENERAL BIOLOGY OF MICRO-ORGANISMS 



The formation of an endospore begins with the accumulation 

 of chromatin granules in one part of the cell, where they coalesce, 

 lose their contained water and seem to become embedded in an oil); 

 or fatty substance and surrounded by a membrane. Very early in 

 the process the spore no longer stains readily. In some forms 

 {Bad. anthracis) the cell in which a spore has formed disintegrates 

 rapidly, set-ting free the spore, while in others {B. tetani) the cell 

 may continue its activities after formation of the spore. The spore 

 germinates when conditions again become favorable to active 

 growth. The new cell may burst the spore wall into halves, or 

 at the end, or the spore wall may soften and become a part of the 

 new growing cell. 



Filterable Viruses. — The difficulty of accurate morphological 

 study is so great as to appear insurmountable in the case of cer- 

 tain microbes which are very definitely recognizable by certain 

 effects which they produce. This is especially true of those living 

 things capable of passing through the fine filters which prevent 

 the passage of small bacteria. The causes of certain diseases 

 exhibit this character, and these have come to be known as filter- 

 able viruses. There can be httle question that non-pathogenic 

 filterable microbes also exist although they seem to have escaped 

 observation. Accurate knowledge of the morphology of many 

 of these forms remains to be disclosed by future, investigation. 

 Meanwhile, the efforts to classify them as bacteria or as protozoa 

 may well be spared. The propriety of including them as living 

 things is, however, only occasionally questioned. 



Protozoa. — The protozoa or unicellular animals have assumed 

 very great importance as causes of disease during the past twenty 

 years. Fortunately for the systematist, the free-living protozoa 

 had received considerable careful study and the larger groups of 

 protozoa had been well defined before the interest in pathogenic 

 properties had the opportunity to over-shadow morphological 

 study. The number and variety of easily recognizable morpho- 

 logical characters presented by the protozoa are greater than 

 those of the bacteria; and the organisrns are, on the whole, larger. 



