GLOSSARY. 725 



Hyaloid. Glass-like; a name given to the delicate membrane inclosing 

 the vitreous humor. 



Hydrocarbons. Compounds of carbon and hydrogen. Fats, though 

 containing oxygen in addition, have been considered as hydro- 

 carbons. 



Hypennetropic. A term applied to eyes in which the focus of parallel 

 rays of light lies beyond the retina ; also called long sight. 



Hypertrophy. Increased growth from excessive nutrition. 



Hypoblast. The undermost of the layers of the blastoderm, from 

 which the pulmonary and alimentary tracts and their glands are 

 formed. 



Infusoria. A name given to a large class of simple organisms which 

 are found in dirty water. 



Inhibition. A checking or preventive action exercised by some ner- 

 vous mechanisms over nerve corpuscles and other active tissues. 



Irradiation. The phenomenon that bright objects appear larger than 

 they really are. It is due to the extension of the effect of light on 

 the retina to those parts immediately adjacent to where the light rays 

 impinge. 



Kymograph. An instrument used for recording graphically the undu- 

 lations of blood pressure, measured directly from a blood vessel by 

 means of a manometer. 



Lachrymal. Pertaining to the secretion of tears. 



Lacunae. Small spaces in the substance of bone tissue, occupied dur- 

 ing life by the bone cells. They appear black in sections of dry 

 bone owing to their containing air, which replaces the . shriveled 

 cells. 



Latency, or Latent period. The time that elapses between the 

 moment of stimulation and the response given by an active tissue. 



Leucin. This is a common product of the decomposition of proteids. 

 It is formed in the later stages of pancreatic digestion. 



Leucocytes. A term applied to the white blood corpuscles and lymph 

 cells. 



Lumen. The open space seen on section of a tube, vessel or glandular 

 saccule ; the cavity surrounded by the gland cells, in which the 

 secretion collects. 



Lymph. The liquid collected by the absorbent vessels from the tissues ; 

 the return flow of the irrigation stream escaping from the blood ves- 

 sels to nourish the tissues. 



