August 6, 1915] 



SCIENCE 



195 



formed but are much smaller than expected 

 shows that partial repulsion exists between the 

 two yellow variations. In the origin of the 

 55 yellow rats which have been tested, 110 

 gametes were involved. Inspection of the re- 

 sults shows that in 92 of these gametes the 

 factors for red-eye and pink-eye remained 

 apart, as they were originally ; but in 18 of them 

 a cross-over must have occurred producing a 

 gamete which contained both factors. This 

 ratio of 92 unchanged to 18 cross-over gametes 

 (or 5.1 to 1) among the gametes which pro- 

 duced the yellow rats, should give nearly, 

 though not quite, the gametic ratio among aU 

 gametes produced by the Ej rats. This true 

 gametic ratio may be shown by the foregoing 

 figures to be about 4.6 to 1 and the per cent, of 

 cross-overs to be about 18. 



Animals of class 3 {pprr), homozygous for 

 both kinds of yellow, should produce gametes 

 in which these two characters would show posi- 

 tive coupling instead of repulsion. This mat- 

 ter is now .being investigated with the idea of 

 finding a quantitative expression for the 

 strength of the coupling and comparing it with 

 the strength of the repulsion already demon- 

 strated. 



W. E. Castle, 

 Sewall Wright 



BussEY Institution, 

 June 28, 1915 



TOXICITY AND MALNUTRITION^ 



The concept denoted by the word " toxicity " 

 contains an element essentially physiological 

 in its nature and describes primarily not so 

 much a chemical property of a given sub- 

 stance as the result of a chemical reaction of 

 this substance with one or more constituents 

 of a given organism. Thus the effects pro- 

 duced by the chemical substance on the organ- 

 ism are obviously due to the chemical prop- 

 erties both of the substance itself and of the 

 tissues of the organism. Hence, while derived 

 in part from the chemical properties of the 

 substance, toxicity does not exist apart from 

 the organism and can be asserted of any given 



1 Published by permission of the Secretary of 

 Agriculture. 



substance only after fitting experiments have 

 been carried out on the organism in question. 

 In contrast to this property, the purely chem- 

 ical properties, such as acidity or alkalinity, 

 exist apart from any relation to the organism. 

 When a given chemical substance possessed of 

 specific properties comes in contact with an 

 organism which of course is essentially made 

 up of substances having likewise definite 

 chemical properties, the reactions which follow 

 in accordance with the laws governing chem- 

 ical behavior are capable of description by 

 means of chemical terms, but from the stand- 

 point of the organism a physiological result 

 has occurred defined not in terms of ions and 

 molecules, but in terms of function. When, as 

 a result of the chemical reaction, the organism 

 is so modified as to eause the non-performance 

 or imperfect performance of function a more 

 or less marked physiological injury is recog- 

 nized. If the injury involves sufficiently im- 

 portant functions and the reaction is irrever- 

 sible, death results. Should functional activity 

 be impaired only in nonessential particulars or 

 should the reaction be reversed, life may per- 

 sist in spite of permanent injury or recovery 

 may take place. If the arrest or derangement 

 of function is sufficiently thorough and prompt, 

 the organism is said, in popular phrase, to be 

 " poisoned " and the chemical substance enter- 

 ing into the disturbing reaction is said to be a 

 " toxic " substance. In view of these consid- 

 erations there seems to be no scientific ground 

 for limiting the term " toxicity " to the pop- 

 ular conception. 



" Toxicity " results in functional impair- 

 meat due to chemical reaction and, accurately 

 speaking, is more a matter of kind than of 

 degree. If this impairment proceeds to the 

 point of death there might seem to be a basis 

 for distinction between this result and that of 

 a less serious injury not so terminating. How- 

 ever, if death takes place indirectly and re- 

 motely through secondary changes initiated 

 by the chemical reaction, the organism would 

 still have been "poisoned." If functional in- 

 jury, however slight and remote, should foUow 

 from the chemical reaction, it would still be in 

 kind a " toxic " action. 



