Irregularly scattered over the face, and in some cases also over the neck, shoulders and upper part of the trunk, are to be seen several, fifty or more, pin-head- to pea-sized papules, tubercles or pustules; commonly the eruption is of a mixed type (_acne vulgaris_), the several kinds of lesions in all stages of evolution and subsidence presenting in the single case. Interspersed may generally be seen blackheads, or comedones. The lesions may be sluggish in character, or they may be markedly inflammatory, with hard and indurated bases. In the course of several days or weeks, the papules and tubercles tend gradually to disappear by absorption; or, and as commonly the case, they become pustular, discharge their contents, or dry and slowly or rapidly disappear, with or without leaving a permanent trace, new lesions arising, here and there, to take their place. In exceptional instances the eruption is limited to the back, and in these cases the eruption is usually extensive and persistent, and not infrequently leaves scars. #What do you understand by acne punctata, acne papulosa, acne pustulosa, acne indurata, acne atrophica, acne hypertrophica, and acne cachecticorum?# These several terms indicate that the lesions present are, for the most part, of one particular character or variety. #Describe the lesions giving rise to the names of these various types.# Blocking up of the outlet of the sebaceous gland (comedo), which is usually the beginning of an acne lesion, may cause a moderate degree of hyperaemia and inflammation, and a slight elevation, with a central yellowish or blackish point results--the lesion of _acne punctata_; if the inflammation is of a higher grade or progresses, the elevation is reddened and more prominent--_acne papulosa_; if the inflammatory action continues, the interior or central portion of the papule suppurates and a pustule results--_acne pustulosa_; the pustule, in some cases, may have a markedly inflammatory and hard base--_acne indurata_; and not infrequently the lesions in disappearing may leave a pit-like atrophy or depression--_acne atrophica_; or, on the contrary, connective-tissue new growth may follow their disappearance--_acne hypertrophica_; and, in strumous or cachectic individuals, the lesions may be more or less furuncular in type, often of the nature of dermic abscesses, usually of a cold or sluggish character, and of more general distribution--_acne cachecticorum_. #What is acne artificialis?# Acne artificialis is a term applied to an acne or acne-like eruption produced by the ingestion of certain drugs, as the bromides and iodides, and by the external use of tar; this is also called _tar acne_. #What course does acne pursue?#