4OO JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS nizing both the existence and the extent of any bacteriostatic ififlu- ence on germicidal test data as de- termined by the standard phenol- coefficient procedure. In general, the method comprises making a subtransfer (4 loopfuls) from the original subtransfer tube. By this sub-subtransfer it is assumed that the toxic material M will be affected through dilution so as to make it no longer capable of acting bacterio- statically. That is M.B =M+B Time does not permit going further here to show certain fallacies in this procedure. Suffice it for our cur- rent purposes merely to mention the fact. Another phase of this b•cterio- static influence on micro-organisms, especially as to how it may cause false interpretations of germicidal test data, was shown by the speaker several years ago. Experimental data were presented then (1) which show how, even though a "-, 0" re- sult is obtained by the standard F.D.A. phenol-coefficient and the Cade-Halvorson plate count modi- fication tests, actually at the end- point time of the test (e.g., at the 10-minute contact time period) many viable organisms are present. These organisms may be considered to be, for the most part, in th'e IM.B[ condition and therefore die off dur- ing the incubation period. How- ever, some of them at least are capable of being neutralized under the influence of a proper antidote and the IM.B.[ = M q- B, setting free the bacteria to grow again. In other words, from the test find- ings it has been assumed that all of the organisms were dead--in real- ity they are not--but are actually in a condition of growing under suitable influences, i.e., they are still potential pathogens. Mention only can be made here, for lack of time, of one more set of conditions which exist in connection with the practical use of bacterio- static substances, as well as an inter- fering influence producing false germicidal test data. This includes the effects, especially, of such sub- stances as quaternary ammonium compounds, wherein some 99+ per cent of the test organisms apparently are truly killed in a short interval of time (even less than 1 minute), but a few bacteria remain viable (even for 30 minutes or more). By the standard F.D.A. phenol-co- efficient procedure a "-" result is always obtained by, say a 1-.q000 level, whereas by using such special techniques as the Klarmann-Wright semimicro method, (2), the Stuart ring or carrier method (3), the Cade swab technique ({), or others, it can be sh9wn , beyond any doubt, that some viable bacteria are still present. The reason for this situa- tion has been attributed by some to the fact that the quaternary compounds possess high bacterio- static properties and, therefore, pro-. duce these results in a manner simi- lar to that described above. That is: 2M q- 2B = M.B + and (M.B q-IM.B[ + 2A 2M.A + 2B).

:'. This, no doubt, is a partial answer :!i)( to the phenomenon in question, but •::-!"in addition--and quite likely to a •'::':' greater degree--there exists in these i!i(:. situations another set of conditions, ?or influences. These are physico- 'j.i chemical in nature, and act to pre- .... ' vent contact between the medica- ,::•: tion and the bacteria by forming a ß film over the latter by some form i !:!::i.: of agglutination of the former by ::::::::: adsorption of either M or B onto i:: :I:'I the glass, metal, or rubber, etc., :,.. !.'•i:i. used as the vessel to contain the mixture, or by the normal clumping .:. of the bacteria themselves as they have grown in the culture, etc. By shaking, swabbing, neutralizing, etc. these uncoatacted, or partially con- tacted, organisms are iater set free ß to be found as viable when the vast majority of the others have been killed. These, no doubt, account for many of the "wild plusses" which show up in our test data and cause so much difficulty in evaluating germicidal potencies of the quater- naries. It should also be brought out here that this phenomenon is not one exclusive for quaternary ammonium compounds. It occurs for many other types, if not all, of germicidal substances, but in most cases to a lesser degree. A descrip- tion of how this fact fits into our general formula will be found above where Chart 4 is discussed. PRACTICAL ASPECTS OF BACTERI0- STASIS Hav{ng shown what bacterio- stasis is and how it works on bac- DETERMINING BACTERIOSTATIC POTENCY OF CHEMICALS 401 teria, we will now present a brief outline as to how the cosmetic and allied industries can make use of these bacteriostatic properties of chemicals. This includes two op- posite approaches, namely: (a) For preservative purposes, wherein the inhibition of some of the normal metabolic processes of the bacterial cell is the goal rather than inhibiting the growth or reproduc- tion abilities of the cell. Thus, the product (cosmetic cream) is "pre- served" and kept from deteriorating from either a chemical or a psy- chological standpoint. Here the effect is outside the cell, i.e., in the substrate. (b) For therapeutic purposes, wherein growth prevention is the basic aim. In the former case it is the product itself that requires the bacteriostatic influences applied to it whereas in the latter case it is th• host on which the product is to be applied, that becomes the main object of interest as far as the effects of the bacteriostatic action is concerned. TEST METHODS FOR BACTERIO- STATIC ACTIVITY In general, the following five procedures are used for the purpose of determining if a product possesses bacteriostatic properties, if it is ex- erting such powers under the specific conditions, or if it is capable of doing the same, and in what limit- ing concentrations. Each method, however, may produce a different answer as to the end-point concen- tration, due to the specific nature of