734 GLOSSARY. 



Sensorium. That part of the nerve centres which is supposed to 

 perceive sensory impressions. 



Somatopleure. The subdivision of the mesoblast which, with the 

 attached epiblast, forms the body-walls of the embryo. 



Specific gravity. The relation of the weight of a given volume of 

 any substance to the weight of an equal volume of distilled water 

 at 4 C. 



Spherical aberration. The different degrees of refraction at differ- 

 ent parts of a lens giving rise to different focal lengths, and 

 causing an indistinctness of the image. 



Sphygmograph. An instrument for obtaining a graphic representa- 

 tion of the pulse- wave by means of a lever applied to the radial 

 artery at the wrist. 



Splanchnopleure. The subdivision of the mesoblast which with 

 the attached hypoblast forms the chief visceral cavities of the 

 embryo. 



Sporadic ganglia. Swellings occurring in the course of the peri- 

 pheral nerves caused by a group of nerve corpuscles. 



Steapsin. A ferment existing in the pancreatic juice which causes 

 or aids the saponification of the fats. 



Sudoriferous glands. The small tubular glands of the skin which 

 secrete the perspiration. 



Summation. The adding together of several single contractions of 

 muscle to form a tetanic contraction ; the accumulation of 

 stimuli. 



Sutures. Unions formed by the direct apposition of bones without 

 intervening cartilage. They do not permit of motion. 



Sympathetic nerve. The ganglionic nervous cord on either side 

 of the vertebral column. It transmits most of the vaso-motor 

 impulses coming from the cerebro-spinal centres. 



Symphysis. A form of joint without sy no vial membrane in which 

 the bones are fixed together by fibro-cartilage. 



Synthesis. The artificial building up or construction of a chemical 

 compound from simpler materials. Natural processes are not 

 termed syntheses. 



Systole. The period of contraction of the heart's muscle. 



Taurocholic acid. An acid existing in combination with soda in 

 the bile of man and of carnivorous animals. 



Tetanus. In physiology is used to denote the prolonged contrac- 

 tion of the skeletal muscles which follows rapidly repeated stimu- 

 lations or nervous impulse. 



