29 
heat began to lose their virulence in thirty days, but at room tempera- 
ture were virulent for mice at the end of ninety days, and in the ice 
chest at one hundred and sixty-live, when all of the material was 
exhausted. 
RESUME AND CONCLUSIONS. 
This study was undertaken and is published on account of its impor- 
tance from a public-health standpoint, particularly in view of the fact 
that glycerin is used to conserve vaccine virus and analogous products. 
On account of its bland and nonpoisonous properties glycerin has long 
been used as a preservative for organic matter; but not until 1891, 
when Copeman claimed for it special virtues as a germicide, did it 
come into general use to purify vaccine virus. 
A false sense of security arose owing to an overestimate of the anti- 
septic and germicidal value of glycerin. This fact we have brought 
out in previous publications on the subject of the bacteriological 
impurities of vaccine virus. Other substances, such as chloroform 
vapor, chloretone, potassium cyanide, carbolic acid, formalin, etc., 
have since been used as a substitute for gljmerin with more or less 
success, and it is possible that one of these more energetic germicidal 
substances may be found to be superior to glycerin for this particular 
purpose in commercial practice. 
The experiments are published in detail at the request of several 
vaccine producers who desire to know the exact value of glycerin as a 
germicide and antiseptic. 
In brief, it may be stated that glycerin has distinct but very feeble 
germicidal and antiseptic properties. The results are summarized as 
follows: 
GLYCERIN AS AN ANTISEPTIC. 
Small quantities of glycerin, less than 10 per cent, added to nutrient 
media have well-known powers of favoring the growth and multipli- 
cation of many forms of bacteria. 
The presence of 50 per cent of glycerin will restrain all bacterial 
growth. Less than this amount can not be depended upon for the 
preservation of vaccines and other organic growths.^ 
The antiseptic power varies for the different glycerins. For in- 
stance, some restrain all growth and development when present in the 
proportion of 43 per cent; others require 49 per cent. 
No evident growth or multiplication of bacteria takes place in nutri- 
ent media containing 32 per cent of glycerin, but molds grow in 
stronger percentages, viz, 40 to 49 per cent. 
In order to prevent the growth and development of pus cocci at 
least 33 per cent of gl}^cerin must be present. This is more than that 
« The percentages throughout this jDaper are by volumes. 
