A BIOLOGICAL PHENOMENON 57 



that the reader may have all the elements which I myself 

 possessed at the beginning of my work in 1915, 



Carrel's experiments represent the first systematic study of 

 these phenomena. They led him to the culture of tissues in 

 vitro, and this second problem caused him to abandon the 

 first. The work was accompHshed at the Rockefeller Institute 

 in New York, and principally on dogs. The wounds were 

 obtained by resecting a piece of skin of geometrical, i.e. 

 rectangular, trapezoidal, or circular, shape. To distinguish 

 the edge of the original wound he preferably employed dogs 

 with a black skin, or else tattooed the outline of the wound 

 on the epidermis with India ink. It was thus easy to follow 

 the evolution of the phenomenon of cicatrization. The 

 dressing consisted in an application of sterile talcum or of 

 hot paraffin wax. The wounds were kept as sterile as possible. 

 It is superfluous to add that all operations were made under 

 complete anaesthesia. 



Under these conditions the following facts were brought 

 forth. Cicatrization passes through four phases or periods. 



1. Quiescent or latent period. This is the period which 

 stretches between the moment of the resection and that when 

 granular contraction sets in. Granulations are small pro- 

 tuberances resembling somewhat a cauliflower, but of a bright 

 red colour. They are generally dry, shiny, and of a healthy 

 aspect on a sterile wound. During these first days the dimen- 

 sions of the wound do not change. Hence the name given to 

 this period, the duration of which is variable in different 

 wounds (one to five days). At the end of that time, the 

 period of contraction suddenly starts. (Fig. i.) 



2. Period of granular contraction. At this moment the edges 

 of the wound begin to come closer together. Very quickly at 

 first, then slower. The rate of this contraction depends on the 

 surface of the wound and not on its age, as was believed until 

 then. In order to demonstrate this clearly. Carrel cut out 

 two rectangular wounds of different sizes on the same dog. 

 The large sides measured respectively 66 and 26 millimetres. 

 In the course of the first 48 hours the length of the larger one 



