18J6.] MICROSCOPICAL JOUBNAL. 157 



with roanded or with blunt ends. In fact, the structure 

 may be varied in innumerable ways. 



The third class, but a few species of which have been 

 studied, may occur as bent rods or comma-shaped organ- 

 isms when found singly, or, when growing opt into 

 threads, may have a spiral or corkscrew appearance (see 

 Fig. 6) The most important germ of this class thus far 

 studied is tire spirillum of Asiatic cholera. 



No hard and fast lines can be drawn, as all these 

 classes gradually merge one into the other. Grrouping 

 and form of all kinds of bacteria are affected to greater 

 or less extent by variations in food and environment. 

 In old cultures, or where the conditions are unfavorable 

 for development, we frequently have irregular li^n-typ- 

 ical germs. These are spoken of as involution forms 

 (Fig. 7). Some germs also develop spores (Fig. 8), cor- 

 responding to the seeds of higher plants, which may give 

 the germ an atypical appearance ; a very .good illustra- 

 tion is the bacillus of tetanus, or lockjaw, in which the 

 spore occurs at one end of the rod, giving the appear- 

 ance, in stained specimens, of short pins. 



One of the most important i^roperties of bacteria, from 

 the biologist's point of view, is the facility with which 

 their protoplasm combines with the basic anilin colors, 

 thereby enabling the observer to study the form and size 

 of the organism with ease and distinctness. In some 

 cases, such as of tubercle bacilli, this reaction is very char- 

 acteristic when some special stain is employed. 



Styined microscopical preparations of the most impor- 

 tant disease-germs, by which to verify their own mounts, 

 are being called for by that class of physicians who have 

 not had the privilege of laboratory instruction, but are 

 alive to the necessity of using all the means within their 

 grasp of making as early and accurate diagnoses of their 

 cases as possible. 



Notwithstanding the many and extensive researches 



