GROWTH AFFECTED BY FEEDING DUCTLESS GLANDS 315 



stance). Pineal substance was given in amounts larger than 

 those fed to guinea pigs (in most cases) by McCord ('14), but 

 in one of McCord's experiments where doses of 100 mgms. of 

 dried substance was used daily, the experimental animals in a 

 given time grew in weight 40 per cent more than the controls. 

 .4.S stated above, there seemed to be no difference in the result 

 with albino rats in the present experiment, whether small amounts 

 of 20 mgms. or larger amounts up to 150 mgms. of dried pineal 

 substance was fed on alternate daj^s. With the larger doses 

 there was no evidence indicating that toxic effects of gastro- 

 intestinal disturbances were produced by the medication. 



As shown in tables 2, 6 and 7, the various rats of the same 

 age and sex are also of nearly the same body-length regardless 

 of treatment. The agreement here is even closer than in re- 

 gard to comparative weights and emphasizes still more strongly 

 the fact that the experimental rats as compared with the con- 

 trols suffered no marked gross body changes on account of the 

 administration of ductless glands. 



The growth records of the individual rats illustrate, as has been 

 pointed out above, that very serious errors might easily creep 

 into the conclusions from an investigation of this kind, which 

 includes animals from several different litters. A preliminary 

 comparison of the individuals in each litter showed negative 

 results, so all were finally grouped as shown in the various tables. 

 There is always, of course, some danger in drawing conclusions 

 from averages, but this danger is slight if the individual data 

 are also carefully studied, and the grouping judiciously made. 



Care must be taken in work of this nature to select experimental 

 and control animals from the same litter and as nearly alike 

 as possible. In many investigations on growth this has not 

 been done. Experimental groups of animals of one sex have 

 even been compared with groups of another sex; or, more com- 

 monly, an experimental group has contained both sexes in a 

 ratio different from that in the control group. 



Finally, the depressing effects upon growth and body weight 

 obtained by some investigators by the administration of ductless 

 glands especially the thyroid (Magnus-Levy, Bircher, Carlson, Far- 



