91 



MEASUREMENT. 

 According lo E b o 1 i n g i'^'') the measiiremciils can only 

 be undertaken indirectly as we have no techni([ue devel- 

 oped at the present time tor directly measuring the actual 

 increase in mass of tissue. In s{)ile of the inaccuracy of 

 the method, many new facts have lieen discovered. When 

 proper care is taken, the Ihickness of the new tissue does 

 not vary and can, Iherefore. be disregarded. The measure- 

 ments of the areas of new tissues can be made in two dif- 

 ferent ways, either by measuring the width of the ring of 

 new cells surrounding the original fragment, or by measuring 

 the area of new growth. The lasl method gives more pre- 

 cise results. About an hour after the cultures have been 

 prepared they are examined under the microscope to see 

 whether they are still in good shape, whether they are cut 

 neatly, whether there is any folding of the edges and 

 whether the coagulation of the new medium has taken place 

 and so on. Then the cultures are placed in a vertical pro- 

 jecting apparatus E dinger and the outline of the frag- 

 ment is traced on a sheet of paper. This operation recjuircs 

 not more than 20 seconds. It is important to avoid over- 

 heating the culture while being projected. After 48 hours 

 incubation a second drawing is made. Of course one has, 

 in many cases, here to judge a little where to make the 

 outline; sometimes the periphery may be a little irregular, 

 and this, naturally, does not mean to trace single cells which 

 may have migrated a little further than the rest of the big 

 mass. If the outlines of the new growth are very irregular, 

 some mistake has been made and the culture should be re- 

 jected. Afterwards the area of the original fragment and the 

 total area after 48 hours are measured with the planimeter 

 and expressed in square centimeters. The total area minus 

 the area of the original fragment is the absolute increase of 

 the fragment. This area, divided by the area of the i)rimi- 

 live fragment, is the relative increase of the fragment. The 

 relative increase cjf the experimental fragment divided by 



