30 



SCIENCE 



[N. S. Vol. XLV. Ko. 1150 



tions, union in fixed and in multiple pro- 

 portions. It is true that in reactions be- 

 tween a weak acid and a weak base there 

 is union in variable proportions, so that a 

 series of compounds are formed. But in 

 general it may be said that in chemical re- 

 actions the results maj^ be foretold when 

 the effect of controllable factors such as 

 dosage, temperature, atmospheric pressure 

 and the like, have been determined. The 

 substance concerned in the reaction, and 

 the conditions that affect it, have been 

 rigorously tested and are understood, so 

 that a given result can always be counted 

 on. The experiment controls itself when 

 properly performed. On the other hand, 

 no one can tell what will happen if he in- 

 jects a million staphylococci into the ear 

 vein of a rabbit. The animal may be dead 

 the next day with no evident lesions; it 

 may die a week later with abscesses in 

 various parts of the body, or it may show 

 no symptoms and recover perfectly. These 

 disparate results are due to the fact that 

 in an experiment of this sort we are con- 

 fronted with two sets of variable condi- 

 tions inherent on the one hand in the living 

 microorganism that is injected and on the 

 other in the experimental animal. We 

 recognize the existence and to some extent 

 the range of certain of these variables, but 

 remain ignorant of many of them; the 

 majority of them are inherent in the con- 

 dition we designate as life and disappear 

 in death. It is incorrect to assert that our 

 ignorance of them is due to an interest in 

 vitalism. "We are free to admit that our 

 science is very young, that our data are 

 relatively few, and that our ignorance of 

 the factors concerned is great. And yet 

 we have a group of significant, reliable and 

 practical phenomena that we can repro- 

 duce at will when we handle these variable 

 factors in our own way. Many of our re- 

 actions, although indefinite from the stand- 



point of chemistry, are of a delicacy that 

 chemistry rarely, if ever, attains. The 

 point of interest here is that the experi- 

 mental methods of present-day chemistry 

 not only have not led us to new facts in 

 our field, but do not help us much to ex- 

 plain or control our present ones. In the 

 experiment cited we can not assert from 

 previous experience exactly with what 

 point in the range of either variable factor 

 we are confronted, we can not previously 

 determiae our conditions and know that 

 they now actually exist. We know in a 

 general way that in the experiment I have 

 outlined we have to deal particularly mth 

 fluctuations in the virulence or pathogen- 

 icity of the staphylococcus concerned and 

 with variations in the resistance to infec- 

 tion in the individual rabbit. Our type of 

 experiment, then, is never complete unless 

 we introduce numerous simultaneous and 

 external controls. In the particular prob- 

 lem I have cited, we find that although one 

 million staphylococci killed Kabbit No. 1 

 yesterday, a subsequent transplantation of 

 the microorganism fails, in the same dose, 

 to kill Rabbit No. 2 to-day. It could be 

 determined that this result is due to a loss 

 of virulence in the microorganism by the 

 introduction of Rabbit No. 3 which is given 

 twice the dose and dies as did No. 1 yester- 

 day. Individual variations in resistance 

 may, to a great extent, be avoided by choos- 

 ing for the experiment rabbits of the same 

 weight, raised under the same conditions, 

 or, better still, from the same litter. 



As a further illustration of the differ- 

 ence in viewpoint between the chemist and 

 ourselves, let me suggest that the tendency 

 of the former on entering our field of 

 activity would be to devise a more precise 

 method of estimating the number of bac- 

 teria used in the experiment rather than 

 to introduce such controls as I have men- 

 tioned. 



