Z CHOICE OF METHODS 



P., J. Exp. Med., 1925, 41, 739-759). The opportunities are many especially 

 in animal experimentation. 



Another way to examine structure in vivo is to record the structure by x-ray 

 photographs and to magnify the photographs, see Microradiographic examina- 

 tion. 



2. To Examine through Windows in Vivo 



The construction of windows in the skin or body wall through which the 

 tissues can be examined in vivo is a less ideal technique because it involves 

 surgical interference with the body. In the most used of these techniques a hole 

 is made through a rabbit's ear from one surface to the other. A glass chamber 

 is then sewed into the hole in such a way that a blood vessel is included between 

 a thin layer of glass (serving as a cover glass) and a thicker one serving as a slide. 

 After a time the epidermis adheres to the edges of the chamber and blood vessels, 

 nerves and other tissues grow into it where they can be studied under oil immer- 

 sion objectives. This technique was first reported by Sandison (J. C, Anat. 

 Rec, 1924, 28, 281) working under Dr. E. R. Clark at the University of Penn- 

 sylvania. It has since been very greatlj'- improved (Clark, E. R., et al., Anat. 

 Rec, 1930, 47, 187-211 and Abell, R. G., and Clark, E. R., Anat. Rec, 1932, 

 53, 121-140) by the introduction of "round table" and "moat" chambers. 



To place a window in the wall of the skull and to observe what is going on 

 within has been done with more or less success on several occasions. The tech- 

 nique devised by Forbes (H. S., Arch. Neurol, and Psych., 1928, 19, 75) permits 

 direct observation at low magnification of the blood vessels over the cerebral 

 convolutions with so little injury that their behaviour in various experimental 

 conditions can be investigated (see also Clark, E. R., and Wentsler, N. E., Proc 

 Assoc. Res. Nerv. and Ment. Dis., 1937, 18, 218-228). Through a window in 

 the thoracic wall Wearn and his associates (Wearn, J. T. et al., Am. J. Physiol., 

 1934, 109, 236-256) have similarly studied the pulmonary arterioles and capil- 

 laries. They employed a fused quartz cone to conduct light to the tissue. For 

 collection of alveolar fluid see Terry, R. J., Anat. Rec, 1926, 32, 223-304; 1936, 

 64, 75. 



Other investigators have availed themselves of the natural \^indow, the 

 cornea, through which what goes on immediately within it in the anterior cham- 

 ber of the eye can be observed. Several tissues have been successfully trans- 

 planted into this chamber. Perhaps the most dramatic is the behavior of trans- 

 planted uterine mucosa in the rhesus monkey. In it the menstrual changes 

 can be seen in detail and the influence of hormones noted (Markee, J. E., Con- 

 trib. to Embryol., Carnegie Inst, of Washington, 1940, 28, 219-308). For some 

 kinds of work the fact that the tissue fluid (aqueous humor) in this chamber 

 differs from others in the same animal by the absence of certain species specific 

 growth inhibiting factors is a priceless asset. Thus Greene (H. S. N., Science, 

 1938, 88, 357-358) was able to grow pieces of human cancers, which ordinarily 

 quickly die in other species, in the anterior chambers of the eyes of some mam- 



