PURE CULTURE METHODS 109 
In case the organism does not produce growth on either of these media at 
either temperature, it should be invigorated with any medium and at any tem- 
perature known to be adapted to its growth. Under such circumstances, 
invigorate by the procedure just outlined but using the medium and tempera- 
ture found most favorable for the organism in question, recording on the chart 
the method of invigoration adapted. If no conditions are known under which 
the organism in question produces vigorous growth, it should be studied without 
preliminary cultivation as soon as possible after isolation from its natural 
habitat. Such an organism is not likely to give good growth on any ordinary 
media, and the results of the study called for by the chart will have little 
significance. 
Motility. Some care is necessary in interpreting the results of 
motility determinations. Positive results are satisfactory but negative 
results are convincing only after a number of attempts. The safest 
method to follow is to make flagella stains for if the organism possesses 
flagella, it is reasonable to assume that it is motile. The Committee 
states that even negative results do not absolutely prove that the 
organism is immotile. 
Vegetative Cells. Some bacteria go into the spore stage so quickly 
that in order to secure vegetative cells, as young a culture as possible 
should be used. For making the various determinations it is necessary 
to have a young and vigorous culture. This may be secured by passing 
it through a process of rejuvenation which should consist of continued 
transferring to a medium which is best adapted for growth. It may be 
necessary to determine the optimum temperature and incubate all 
cultures at this temperature. 
Endospores. These may usually be observed on the smears which 
have been stained with the ordinary alcoholic-aqueous stains. On 
account of a different type of protcplasm, possibly, they resist the 
staining process and appear on the smear as colorless bodies usually 
round or oval in shape. In some cells they will be observed in the 
ends or middle. In this case the cell has not decomposed to set them 
free. Special stains may be used for indicating the presence of spores, 
the procedure for which has been given in the Chapter on Staining. 
Very often these special methods are not attended with much success. 
Another method which is often reliable is to kill the vegetative 
cells by heating in broth culture for thirty minutes at 80° C. If after 
this procedure growth is secured by subculturing into other media, 
it is good indication that the culture was a spore former. 
Capsules. The presence of capsules may be indicated either by 
special staining procedures or the growth in the common media. The 
