1915] Johnson: The Vultivation of Tissues from Ampltibians 59 



enlarged it touched about midway an outgrowth, causing its activity 

 immediately to be increased very greatly. This part of the outgrowth 

 was more slender than its base. A.s there is no difficulty in performing 

 this experiment it was tried several times, with always the result that 

 if bacteria attacked the outgrowth other than at tip they acted as a 

 stimulant for increased growth for about a day. 



ilany cultures were made in order to determine somewhat accur- 

 ately the proper length of time that should elapse on the average 

 between retransplantation of tis.sue from one drop of serum mixture 

 to another. This was done by taking careful ob.servation of the appear- 

 ance of the cells; by noting the rapidity of reawakening of activity 

 after being left different lengths of time in a drop of serum mixture, 

 and lastly by observing the beating heart tissue. 



The first two observations showed that two to four days is the 

 proper length of time, but varying slightly with kind of ti.s.sue and 

 temperature. The heart tissue observations perhaps gave more 

 definite light along this line. The number of beats I thought would 

 be lowered with the increased toxic condition of the medium resulting 

 from katabolism. The temperature was kept to see if parts of heart 

 tissue of the embryo responded to heat as does the adult heart. 

 Results showed that there is a close relationship between the condition 

 of the blood serum, temperature and rate of the heart beat. On 

 February 21 at 4 :30 p.m. heart tissue put up four days previously 

 was noticed beating at the rate of 29 times per minute and regularly ; 

 at 8 :30 .\.M. of the next day it had dropped to 16 times per minute 

 but still beating regularly ; at 11 :30 a.m. of the same day it had slowed 

 down to 14 times per minute and was beating very iri-egularly. vary- 

 ing from three to six seconds between beats. This tissue was bathed 

 in Ringer's solution for fifteen minutes and retransf erred for the first 

 time at about noon. By 8 :00 .\.m. of the next day it had gained to 

 34 times per minute, beating regularly ; by 9 -.30 a.m. of the following 

 day it had increased to 38 times per minute; at 11:30 a.m. to 42 times 

 per minute. Here I think it would have reached its maximum rapidity 

 had the temperature remained the same in afternoon as in morning. 

 At 1 :30 P.M. it had decreased to 40+ times per minute, but the decline 

 was counteracted by the ri.se of temperature in the afternoon of about 

 twelve degrees. This increase of heart beat was evident each afternoon. 

 According to this, heart tissue at least, and possibly most others also, 

 ought to be washed in Ringer's solution and changed to a new drop 



