142 THE BACTERIAL CONTENT OF MILK 



tion is due to the opposite of favourable or optimum conditions. 

 In short, that when a bacillus forms a spore it does so because 

 it finds itself amid unfavourable conditions, and sporulates in order 

 to carry on its species by means of more resistant forms. We 

 think there is considerable evidence in support of this theory. 

 Not a few of the lower forms of life in both animal and vegetable 

 kingdoms have more or less analogous conditions of sporulation ; 

 for example, some of the Protozoa and Saccharomycetes. In 

 the latter, multiplication by budding goes on so long as they are 

 well supplied with food. If the supply of nutriment fails they 

 sporulate,^ 



It should be understood that whilst holding the view that 

 spores are a resting stage during adverse conditions, we fully 

 recognise that certain favouring external conditions are essential 

 to spore formation. Of these, there are at least three of which 

 bacteriologists have knowledge, namely, moisture, oxygen, and a 

 certain temperature. Fluid media form an excellent nidus for 

 sporulation so long as some oxygen can gain access to the sporu- 

 lating germs. But many organisms will not sporulate if lying 



1 Yeast can be effectually starved by cultivating on a small block of plaster- 

 of-Paris kept moist under a bell jar ; under these circumstances the yeast is 

 supplied with nothing but water. In a few days the protoplasm of yeast-cells 

 thus circumstanced becomes filled with vacuoles and fat cells. The protoplasm 

 has been undergoing destructive metabolism, and, there being nothing to supply 

 new material, has diminished in quantity and at the same time been partly con- 

 verted into fat. Both in plants and animals fatty degeneration is a more or less 

 constant phenomenon of starvation, and to this bacteria are no exception. 

 After a time the protoplasm collects towards the centre of the cell, and divides 

 simultaneously into four masses arranged like a pyramid of four billiard balls, 

 three at the base and one above. These are the ascospores, and sooner or 

 later they are liberated by the rupture of the mother cell wall. Certain of the 

 Streptothrix family also "sporulate" when they find themselves, like yeast 

 upon gypsum, surrounded by an unfavourable environment. Again, in old 

 cultures, it will be found that when the food supply has been exhausted the 

 bacteria have either sporulated or have died. For these reasons sporulation 

 may be looked upon not as a method of multiplication but one of reproduction, 

 of carrying on the species under adverse conditions. With regard to the rapid 

 formation of spores under apparently favourable circumstances {B. filamentosus, 

 B. anthracis, etc.), it must be borne in mind that the medium may not be by 

 any means so favourable as appears to be the case (Fliigge) It is clear that 

 the food supply immediately around many of the bacteria in a culture must 

 soon be exhausted. Besides there is the toxic influence early at work, often 

 as an inimical agency acting unfavourably towards the bacillus producing it. 

 So that the appearance of spores in such a culture may still be due to condi- 

 tions which are actually unfavourable. 



