December 24: 11 a. m., received 0.87 gram of caffein (0.2009 gram per kilo); 4 p. m., no symptoms. It will be observed that the only effect produced in dog 33 by feeding caffein was increased intestinal putrefaction, although 2.37 grams of caffein were given in three days. Additional data on the effects of the age of animals on the resistance to caffein seemed desirable. The following experiments were therefore carried out. Six puppies of the same litter were weaned when 7 to 8 weeks old and put on a milk diet. Three of them received this diet throughout the experimental period. Meat was substituted in the other three a few days before the administration of caffein was begun, and was continued until the end of the experiment. Caffein was given by mouth; the initial dose, which was administered for several days and then gradually increased, being 160 to 200 mg for each dog, except one, which received only 100 mg per kilo for several days and then an increased amount. An intermission of a few days (during which no caffein was given) was allowed. This was done on account of some studies carried on at the same time on the effect of caffein on certain constituents of the urine. PUP NO. 1. ---------+---------+--------+-------------+-------------------------- | | | Treatment | Date. | Weight. | Food | (2 per cent | Symptoms. | |(milk). | caffein). | ---------+---------+--------+-------------+-------------------------- | _Grams._| _cc._ | _cc._ | Apr. 21 | 1,450 | 300 | 10.0 | No symptoms. Apr. 22 | 1,520 | 300 | 10.0 | Do. Apr. 23 | 1,450 | 250 | 10.0 | Do. Apr. 24 | 1,375 | 250 | 10.0 | Do. Apr. 25 | 1,420 | 250 | 10.0 | Do. Apr. 26 | 1,390 | 250 | None. | Apr. 27 | 1,400 | 250 | None. | Apr. 28 | 1,405 | 250 | None. | Apr. 29 | 1,420 | 250 | None. | Passed worms. Apr. 30 | 1,430 | 250 | None. | Do. May 1 | 1,450 | 250 | 10.0 | No symptoms. May 2 | 1,515 | 250 | 15.0 | Do. May 3 | 1,475 | 250 | 15.0 | Do. May 4 | 1,495 | 250 | 15.0 | Do. May 5 | 1,515 | 250 | 22.0 | Seems dull and whines. May 6 | 1,535 | 250 | 20.0 | Whines. May 7 | 1,525 | 250 | 20.0 | No symptoms. May 8 | 1,530 | 250 | 20.0 | Do. May 9 | 1,500 | 250 | 23.0 | Diarrhea; passed worms; | | | | tremor and rigidity of | | | | legs; whines. May 10 | 1,490 | 250 | None. | Completely recovered from | | | | the effects of 9th. May 11 | 1,535 | 250 | 25.0 | Can not balance itself;