124 CARNEGIE INSTITUTION OF WASHINGTON. 



is now opened up and, what is most important, the study has ah-eady 

 progressed far enough to make it reasonably sure that the results may actually 

 be obtained." 



EXPERIMENTAL MODIFICATION OF THE GERM-PLASM. 



The attempt to induce changes in the germ-plasm of rats by means of 

 alcohol vapor, described fully in the Year Book for 1915, page 130, has 

 been continued by Dr. MacDowell. An abstract of his work to that 

 date was published in Science, November 12, 1915, and is reprinted here: 



"The purpose of this investigation is to compare the mental capabilities of 

 rats whose parents were alcoholic with those of rats of normal parentage. 

 It is commonly claimed that, in man, the children of alcoholics are less teach- 

 able than children of normals. However, the exceeding difficulty of obtaining 

 genetically comparable controls in man makes the study of a lower animal, 

 although vastly different psychologically, of great interest, since double first 

 cousins — the closest relationship possible for such comparisons — can be 

 used. The first criterion used for judging mental activity has been habit for- 

 mation in a Watson puzzle-box. The habit to be learned consists of a trip 

 to the rear of the box, breaking an electric circuit, and so opening the 

 front door, and, returning to the front, entering the box for the reward of 

 food. The data recorded consist in the times required to open and enter the 

 door of the puzzle-box. Each rat has been given 225 trials; 145 rats have been 

 employed in this training. The data, summarized in various ways, have 

 been represented by graphs. Awaiting the results of a second set of training 

 experiments of a different nature, which are being conducted as a check on the 

 first method, no general conclusions are given and only provisional conclusions 

 are drawn about the present work." 



The following additional conclusions have been reached: 



"First, it is clear that breathing the fumes of alcohol for 90 minutes a day 

 for 100 days does not cause rats to produce young with any sort of physical 

 abnormalities that can be observed. It has also been determined that, for 

 judging the mental valuations, different tests may give opposite results, and 

 the most closely related pairs of families may give opposite results, even when 

 tested by the same method. In the light of these facts it immediately becomes 

 apparent that no final answer to the main problem can be justified until the 

 relative values of the different tests have been established and something is 

 known of the range of variations in mental ability that may be normally 

 inherited in white rats. 



"In support of the above conclusions the following examples are cited: 

 Experiment I includes a litter of rats from normal parents and one from 

 alcoholized parents. The fathers were brothers, the mothers sisters, so that 

 the offspring were double first cousins. Experiment II includes two corre- 

 sponding litters, similarly related, from normal and alcoholized parents. 

 Moreover, the fathers in this experiment were brothers to the mothers in 

 experiment I. Therefore the relationship between the normal litters in 

 experiments I and II was just as close as that between the two litters in each 

 experiment; they were all double first cousins, all from the same grandparents. 



"However, although the alcoholized parents in both experiments were 

 similarly treated, and although the training of all the offspring was alike, in 

 experiment I the training with the puzzle-box showed from every standpoint 

 that the rats from the alcoholized parents were more successful than the rats 



