210 LABORATORY EXERCISES IN BACTERIOLOGY. 



method. Dry and examine in oil without cover. Note the shape of the 

 individual organisms; and after comparison, note the results of use of 

 Gram's stain. 



Exercise 42. From fresh gonorrheal pus repeat the above exercise. 

 Note the gonococci lying in small groups in the cells in the preparation. 

 Note shape of the organisms. Has Gram's method been successful? 



Exercise 43. From a known culture of Bacillus typhosus repeat exer- 

 cise 41. Note the shape of the organisms. Has Gram's stain been suc- 

 cessful ? 



Exercise 44. From a known culture of Microspira comma repeat exer- 

 cise 41, using as the staining solution for the first film a dilute (i : 10) solu- 

 tion of carbol-fuchsin for five or ten minutes with gentle heat. Note the 

 shape of the organisms. Does Gram's method succeed? 



2. Grouping of Bacteria. The occurrence of bacteria in peculiar arrangement 

 is usually the result of incompleteness of separation in the cellular division of the 



& 





G 



FIG. 60. GROUPING OF BACTERIA. 



A. Micrococci. B. Diplococci. C. Streptococci. D. Sarcinae. E. Tetrads. F. Chains 

 of rods (streptobacilli). G. Chains of curved rods (spirochaetse). 



ordinary vegetative mode of reproduction. In multiplication in this manner the cells 

 may divide in one, two, or three planes. In the first case the individuals, if not com- 

 pletely parted, remain placed end to end, chains or filaments being thus produced ; 

 in the second, division occurring laterally and longitudinally, films or merismopediae 

 (sing., merismopedia) are produced; in the third, division taking place in length, 

 breadth, and thickness, packet forms (sarcina) or massive, irregular groups (zoogle&r 

 sing., zooglea) are formed. Such grouping may be often seen in unstained prepara- 

 tions, as in the hanging drop, but best in well-stained films. In staining so as to 

 make clear the delicate lines of division between the individuals of such groups, it is 

 advisable, after having fixed the film by heat, to immerse it for a minute or less in a 

 weak (four per cent.) solution of acetic acid. The best stains are accomplished by 

 very dilute staining solutions left in contact with the film for a prolonged period (one 

 of ordinary stain to four of distilled water, left in contact with the film for ten or fifteen 



