398 JOURNAL OF THE SOCIETY' OF COSMETIC CHEMISTS BACTERIOSTASlS We now see how bacteria are brought into being, how they main- tain their existence, and how they can be removed from man's environ- ment, at will, by means of the proper use of the proper chemicals. Whether the action so produced is a germicidal one, an antiseptic one, or a bacteriostatic one, depends upon a variety of factors. The same chemical can be used to produce all cedure or situation desired by mak- ing the proper choice of chemical, its concentration, etc. To express this in a simple graphic form we present the following theo- retical reaction. It should be borne in mind that this represents onl 7 a simplified situation, so selected as to make the basic problem of bac- teriostatic activity clearer. We do not infer that this is an actual, or the only, reaction, that may be Chart 4.--Equation of Bacteriostasis (i) Mq- Bq- © = (Medication) + (Bacteria) q- (Protected cells) = M.B q- M.B + IM.BI + True bacterio- ' Pseudobacteriostasis stasis, as in A loose A re•rersible spore formation reversible combination combination with the of chemical intracellular and surface enzyme, or enzyme other com- ponent part of the cytoplasm (2) M.B + IM.B.I + 2A = 2M.A 2B (3) M.B q- dilution or washing = M q- B (4) B q- remo•ral of "binding material" O = B Germicidal action. Irreversible combination denaturing the "essential life-unit" three of these conditions, as well as the pseudobacteriostatic one, by varying the concentration employed, the time and temperature of contact, etc. In addition, some chemicals are of such a structure that they can attack those parts of the living cell which produce the mild bacterio- static action, while others combine more or less immediately to produce germicidal actions, with all types of possible variations in between. One thus is able to regulate the pro- going on. Many combinations of these end products are naturally possible. That is, a chemical as used might cause a direct conver- •::. sion of all of the B to the M-----•.B or there may be a situation in which all of the B becomes only M.B, in which condition it can bring about, through indirect methods, a starva- tion of the B so attacked. Thus, ß the end reaction would still be all as . "

DETERMINING BACTERIOSTATIC POTENCY OF CHEMICALS 399 In offering this equation as a graphic exhibition of how bacterio- .: stasis may be brought about, and ::What effects it may eventually pro- duce, bsth on or in the cell as well as in the substrate, we make use of •the following assumptions. First, that the reaction between the bac- teria (B) and the chemical or medi- cation (M) is a simple stoichiometric one of the monomolecular reaction type, wherein one molecule of the •.. chemical reacts with one molecule :, of the cell constituents. We also assume that M is always in excess, .:•:. as would be the case if we have com- plete bacteriostatic or germicidal action. Furthermore we assume, as is actually present in use, that there exists in the medication- bacteria complex some organisms which do not get in contact with the medication because of such physico- chemical factors as film formation, agglutination, adsorption, clumping, etc., and thus do not react the same as far as killing or bacteriostasis is concerned, at least during the same time qnterval. Such organisms are represented as © and thus appear on both sides of the equation. The sum of the amounts of B on the right side of this equation must, naturally, equal 100 per cent of that which entered the reaction at the start (represented on the left). In just what proportion the total B is divided varies as described above. For the purpose of our discussion here we assume that little or none of the organisms exist in the spore form (M.B or true bacteriostasis), but that in the presence of high dilu- tions of certain chemicals the great majority of the cells will be as repre- sented by M.B. These eventually with time may become IM.BI and finally • when the cell dies (Chart 2, curve 3b). Or, eventually the cell by its own repair mecha- nism may neutralize the M and re- pair the damage done by the M.B q- IM.BI combination, acting over the extended period of time. Thus, M.A is formed and B is set free, ready to start reproducing again. (Chart 2, curve 3a). This explains the misnomered "Recovery from death" phenome- non and shows how it is brought about. That is, if during the time interval between where M.B and [ M.B ] are present, and before •--• is reached there is added an anti- dotal substance A to the mixture, it will bring about the reaction M.B q- [M.B Iq- 2A = 2B q- 2M.A (eq. 2, Chart 4). Thus the cell will eventually become free to grow once more. Practical conditions as represented here have occurred in the recent past in connection with the use of mercury compounds. These were formerly thought to be highly germicidal, but now have been found actually to be highly bacteriostatic and not germicidal in anywhere near the previously reported concentrations. In this same connection, so as to make this picture more complete, we wish to make a brief mention of the "Shippen technique," used for many years as a means for recog-