576 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



has demonstrated that a small piece of thyroid may die if exposed to 

 the drying action of the air for more than 10 seconds. Therefore, 

 the section and the handling of the tissues must be very rapid, other- 

 wise the tissue is killed. The dissection of the tissue may be made in 

 a drop of serum, in order to prevent that accident. 



The small cultures are similar to those used by Harrison: One or 

 two small pieces of tissue are transferred to a cover glass and quickly 

 covered with a drop of plasma. It is best to spread the plasma in a 

 thin layer over the cover glass. This is done with the needle before 

 coagulation occurs. The cells grow, then, in a few planes and in areas 

 about the tissue. If the drop is thick the cells grow in many planes 

 and it is difficult to measure the area of growth or to photograph and 

 observe the growing cells. The cover glass is then inverted over a 

 hollow slide with paraffin to prevent drying. The finished slide is 

 immediately placed in a small electric incubator which is used for 

 transferring the cultures from the operating room to the large incu- 

 bator in the room where the study of cultures is made. Coagulation 

 of the plasma takes place either immediately upon the addition of 

 the tissue or soon after the slides are placed in the warm oven. 



To grow tissues on a large scale, the same general technique is used. 

 A rigid asepsis here is most necessary, as it is very easy to infect these 

 large cultures. An entire chicken fetus of 15 days, or small mam- 

 malian fetuses cut into small fragments, may be used for these cul- 

 tures. These fragments are spread in a thin layer over the surface 

 of a large black glass plate and covered quickly with fluid plasma. 

 As soon as coagulation of the plasma has taken place the plates are 

 placed in glass boxes with cotton sponges soaked in water, which pre- 

 serve the proper humidity. The boxes are then carefully sealed with 

 paraffin and kept in such a position that the fluid products of the 

 culture may drain to the bottom. 



During their growth, the cultures can be removed from the incu- 

 bator for a few seconds without danger to their life. Certain tissues, 

 like malignant tumor or spleen, grow and extend so widely that their 

 condition can be observed without the use of the microscope. On 

 a hollow slide, the new tissue of a culture of spleen appears as an 

 opalescent area surrounding the primitive fragment. Even the be- 

 ginning of growth can be diagnosed by the appearance on the sharp 

 edges of the fragment of a very faint and narrow gray band. In 

 the culture on plates the appearance of a whitish color around the 

 fragments of the tissues shows that they are growing. But it is 

 safer to make a few control cultures in hollow slides and to observe 

 their growth with a microscope. 



For the study of the cultures we use a microscope placed in a warm 

 stage, the temperature of which is kept constant. The slides can 



