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The article on the stone louse [Petrophaga lorioti] is probably the most famous entry in one of the De Gruyter publishing house's most frequently sold works: The Pschyrembel Klinisches Wörterbuch. It is one of the most loved entries of the De Gruyter staff and a perfect example of a fictitious article.

As is widely known in Germany, the stone louse article is a tribute to Vicco von Bülow (or: Loriot), the German popular comedian who first presented the small creature with the large teeth to a global public in 1976.

It soon became clear that the discovery was sufficiently important to be included as an entry in the large clinical dictionary.

The following entry therefore appeared for the first time in the 1983 edition of the Pschyrembel:

Stone louse.
Lat. Petrophaga lorioti; native rodent belonging to the lapivora family (♂♂ 0.2-0.3 mm; ♀♀ 0.3-0.4 mm, somewhat larger during gestation), the existence of which has been documented (see Fig.) only in recent years (1983). Whereas the common stone louse is rarely studied, certain human pathogenic variants of the species are of increasing medical interest: the kidney stone louse (P. nephrotica), bladder stone louse (P. vesicae), gall stone louse (P. cholerica), and more recently also the salivary stone louse (P. salivatoria), the (etiological?) function of which in urolithiasis, cholelithiasis and sialolithiasis still requires clarification. The stone louse is unlikely to be of therapeutic use at the present state of knowledge; cf. chemical litholysis, lithotripsy.

Study of the corresponding entries in subsequent editions of the clinical dictionary reveals that the international research community did not tire of advancing new findings concerning the stone louse.

If the Pschyrembel is to be believed, the stone louse is now even responsible for social phenomena. 

Stone louse

Smallest native rodent (size: 0.3–3 mm) in the lapivora family;
ubiquitous, generally apathogenic, mood-enhancing endoparasite (Figure 1); first described 1983;

Clinical significance
  1. Endemic incidence of pathogenic atyp. variants, including
    a)  Petrophaga lorioti parlamentarii: causes elective blue-yellow colour blindness (tritanopie; see colour blindness), detectable by quorum sensing (cave: low diagnostic sensitivity; "5% limit") or molecular genetics (mutation in the GroKO gene; coded for stone louse-specific FTPase); therapy: generally self-limiting;
    b)  Petrophaga lorioti prismi; clin.: whistling face syndrome ("whistle-blower"; see dysplasia cranio-carpo-tarsalis); diagn.: systematic auscultation by medical specialists; reportable disease with suspension of data protection provisions; warning: no presence of NSA(R) owing to the risk of a disorder of the central auditory system;
  2.  Therapeutic use within osteophytolytic stone louse therapy with exploitation of the elevated litholytic capacity of stone louse species at elevated basal temperature resulting from climate warming;
  3.  Use as a vector for myocytic gene therapy (Petrophaga lorioti alipogenti parvoveci).

The phenomenon of stone louse phobia has of course been mentioned in the Pschyrembel Psychiatrie, Klinische Psychologie, Psychotherapie (Psychiatry, Clinical Psychology, Psychotherapy), and users of the Pschyrembel Premium Online database have long been able to study the timid creature in one of the rare video recordings made of it.