290 HISTOLOGY OF THE MORBID PROCESSES. 



nective tissues of the body, in which the usefulness of the tissue 

 resides in its physical properties. In muscular individuals the bony 

 ridges giving attachment to the tendons are more strongly accen- 

 tuated than in those whose muscles are less highly developed. 



A very familiar illustration of functional hyperplasia is furnished 

 by the skin of the palms. Manual labor that is habitual occasions 

 a thickening of the epidermis due to hyperplasia ; exceptional over- 

 work causes damage leading to inflammation, blisters. 



2. Developmental Hypertrophy. Hypertrophy of a part occasion- 

 ally arises without assignable cause and apparently as a mere anomaly 

 in development. Such structures as horns and warts are examples 

 of this form of hypertrophy, which are not readily separated from 

 the group of growths called tumors. When the growth is limited 

 and not progressive it may in most cases be attributed to this form 

 of hypertrophy ; when apparently unlimited, progressive, and atyp- 

 ical in structure, it must be classed among the tumors. 



3. Inflammatory Hypertrophy. Under the influence of damaging 

 agents which act with such mitigated intensity that their effect upon 

 the cells amounts merely to a decided irritation, the formative 

 powers of the cells may be stimulated and an enlargement of the 

 part be brought about, either as the result of hypertrophy or of 

 hyperplasia of its elements. This form of hypertrophy is nearly, 

 if not quite, equivalent to the results of chronic productive inflam- 

 mations, for an account of which the student is referred to another 

 chapter. In cases where the evidences of damage are inappreciable 

 the process may be considered as irritative hypertrophy or hyper- 

 plasia ; where they are at all marked, it must be regarded as inflam- 

 matory. 



The microscopical evidence of hypertrophy is found in an increase 

 of size in the elements composing the tissue. It is not a simple 

 matter to decide from a microscopical examination whether hyper- 

 plasia exists or not, for the microscopical appearances are almost, if 

 not quite, normal. It is often necessary to consider the changes in 

 the gross appearances of the part in order to determine whether its 

 constituent elements have increased in number or not. 



