212 



LABORATORY EXERCISES IN BACTERIOLOGY. 



minutes). Impression films here find their particular use, and should in any doubtful 

 case be resorted to. 



From peculiar modes of grouping which are more or less characteristic, these 

 special terms are commonly applied: When cocci occur singly, the individuals are 

 spoken of as micrococci (a) ; when in twos, as diplococci (b) ; when in chains, as strepto- 

 cocci (c) ; in packets of eight or geometric multiples, as sarcina (d) ; when in planes 

 of four, tetrads (e) (Fig. 60). The term staphylococcus was first applied to cocci whose 

 gross colonies presented a fancied resemblance from their lobulated outlines to a bunch 

 of grapes; later, the idea of small microscopic clusters of the individual cocci became 

 attached to the name. The term has no real place in terminology, the same idea 

 being conveyed by the common term "elumps,"or zooglea. When rod-shaped forms occur 

 in chains, one usually uses the term chains or threads of bacilli, etc., although occasionally 

 the prefix " strepto-" is applied (e. g., streptobacilli}. The term spirochceta is applied 

 where a single long spiral or spiral chain of short curved elements exists. 



Exercise 45. Examine preparations of exercise 42 carefully for apprecia- 

 tion of the diplococcus shape of the gonorrheal organism; and that of 

 exercise 44, with a view of meeting with spirochaeta- 

 like chains of the short comma-shaped individuals. 



Exercise 46. Prepare an impression film from a 

 colony of Bacillus subtilis, and a second film of the 

 same organism by the ordinary method. Stain each 

 with ordinary aqueous solution of fuchsin or gentian 

 violet. What differences are apparent? 



Exercise 47. From some sputum from a chronic 

 tuberculous patient with pulmonary cavities prepare 

 a film, and stain with carbol-fuchsin and Gabbet's 

 solution ; and examine preparation for tetrads (Micro- 

 coccus tetragenus) ; afterward examine the red Myco- 

 bacteria tuberculosis for branching forms. 



A 



B 



FIG. 61. STRUC- 

 TURE OF A BAC- 

 TERIUM. (After 

 Migula.} 



A. Cell membrane. 

 B. Protoplasm. C. 

 Vacuole. D. Me- 

 tachromatic gran- 

 ules. 



3. Structure of Bacteria. The bacterial cell is composed 

 of a cell membrane, a layer of protoplasm, and a central fluid 

 substance. It is not definitely established that bacteria 



possess nuclei, but after proper staining there are likely to be found in the proto- 

 plasm of the cells certain granules which by some are regarded as of nuclear 

 character. From their coloring reactions they are sometimes spoken of as meta- 

 chromatic granules. They are not ordinarily seen. The cell membrane is generally 

 thin, but in some cases it is thick and not well defined on the outer surface, giving the 

 appearance of a mucous envelope or capsule (whence the class of "capsule bacteria"}, 

 and is not readily and clearly stained by the ordinary methods. Such capsules, more- 

 over, are not apt to appear in bacteria grown in the ordinary media, but are best seen 

 when the organisms are obtained directly from the animal body or when grown in 

 fluid blood-serum or a few other special laboratory media. The term ascococci (sing., 

 ascococcus} is applied to the globular forms presenting such encapsulation; in other 

 forms the name capsule bacteria is usually used (Fig. 62). 



The outer surface of the cell membrane in the majority of bacteria, especially in 



